And this is the XSetInputFocus call sending the offending request (on the same system).
(gdb) bt #0 0x00007ffff6cfb350 in XSetInputFocus () at /lib/x86_64-linux-gnu/libX11.so.6 #1 0x00007ffff7eec2c1 in _gdk_wm_protocols_filter (xev=0x7fffffffd8e0, event=<optimized out>, data=<optimized out>) at ../../../../../gdk/x11/gdkdisplay-x11.c:1473 #2 0x00007ffff7ef104f in gdk_event_apply_filters (xevent=xevent@entry=0x7fffffffd8e0, event=event@entry=0x555555a185e0, window=window@entry=0x0) at ../../../../../gdk/x11/gdkeventsource.c:79 #3 0x00007ffff7ef137b in gdk_event_source_translate_event (xevent=0x7fffffffd8e0, event_source=0x555555629340) at ../../../../../gdk/x11/gdkeventsource.c:198 #4 _gdk_x11_display_queue_events (display=0x555555616020) at ../../../../../gdk/x11/gdkeventsource.c:341 #5 0x00007ffff7eb90e4 in gdk_display_get_event (display=display@entry=0x555555616020) at ../../../../gdk/gdkdisplay.c:441 #6 0x00007ffff7ef10e6 in gdk_event_source_dispatch (source=<optimized out>, callback=<optimized out>, user_data=<optimized out>) at ../../../../../gdk/x11/gdkeventsource.c:363 #7 0x00007ffff718e17d in g_main_context_dispatch () at /lib/x86_64-linux-gnu/libglib-2.0.so.0 #8 0x00007ffff718e400 in () at /lib/x86_64-linux-gnu/libglib-2.0.so.0 #9 0x00007ffff718e4a3 in g_main_context_iteration () at /lib/x86_64-linux-gnu/libglib-2.0.so.0 #10 0x00007ffff7501fe5 in g_application_run () at /lib/x86_64-linux-gnu/libgio-2.0.so.0 #11 0x00005555555727e0 in main (argc=2, argv=0x7fffffffdcb8) at demo-Gtk.c:5365 (gdb)